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FreeBSD-SA-09:09.pipe                                       Security Advisory
                                                          The FreeBSD Project

Topic:          Local information disclosure via direct pipe writes

Category:       core
Module:         kern
Announced:      2009-06-10
Credits:        Pieter de Boer
Affects:        All supported versions of FreeBSD.
Corrected:      2009-06-10 10:31:11 UTC (RELENG_7, 7.2-STABLE)
                2009-06-10 10:31:11 UTC (RELENG_7_2, 7.2-RELEASE-p1)
                2009-06-10 10:31:11 UTC (RELENG_7_1, 7.1-RELEASE-p6)
                2009-06-10 10:31:11 UTC (RELENG_6, 6.4-STABLE)
                2009-06-10 10:31:11 UTC (RELENG_6_4, 6.4-RELEASE-p5)
                2009-06-10 10:31:11 UTC (RELENG_6_3, 6.3-RELEASE-p11)

For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:http://security.FreeBSD.org/>.

I.   Background

One of the most commonly used forms of interprocess communication on
FreeBSD and other UNIX-like systems is the (anonymous) pipe.  In this
mechanism, a pair of file descriptors is created, and data written to
one descriptor can be read from the other.

FreeBSD's pipe implementation contains an optimization known as "direct
writes".  In this optimization, rather than copying data into kernel
memory when the write(2) system call is invoked and then copying the
data again when the read(2) system call is invoked, the FreeBSD kernel
takes advantage of virtual memory mapping to allow the data to be copied
directly between processes.

II.  Problem Description

An integer overflow in computing the set of pages containing data to be
copied can result in virtual-to-physical address lookups not being
performed.

III. Impact

An unprivileged process can read pages of memory which belong to other
processes or to the kernel.  These may contain information which is
sensitive in itself; or may contain passwords or cryptographic keys
which can be indirectly exploited to gain sensitive information or
access.

IV.  Workaround

No workaround is available, but systems without untrusted local users
are not vulnerable.  System administrators are reminded that even if a
system is not intended to have untrusted local users, it may be possible
for an attacker to exploit some other vulnerability to obtain local user
access to a system.

V.   Solution

Perform one of the following:

1) Upgrade your vulnerable system to 6-STABLE, or 7-STABLE, or to the
RELENG_7_2, RELENG_7_1, RELENG_6_4, or RELENG_6_3 security branch
dated after the correction date.

2) To patch your present system:

The following patches have been verified to apply to FreeBSD 6.3, 6.4,
7.1, and 7.2 systems.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

# fetch http://security.FreeBSD.org/patches/SA-09:09/pipe.patch
# fetch http://security.FreeBSD.org/patches/SA-09:09/pipe.patch.asc

b) Apply the patch.

# cd /usr/src
# patch < /path/to/patch

c) Recompile your kernel as described in
<URL:http://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
system.

VI.  Correction details

The following list contains the revision numbers of each file that was
corrected in FreeBSD.

CVS:

Branch                                                           Revision
  Path
- -------------------------------------------------------------------------
RELENG_6
  src/sys/kern/sys_pipe.c                                       1.184.2.5
RELENG_6_4
  src/UPDATING                                             1.416.2.40.2.9
  src/sys/conf/newvers.sh                                  1.69.2.18.2.11
  src/sys/kern/sys_pipe.c                                   1.184.2.4.2.2
RELENG_6_3
  src/UPDATING                                            1.416.2.37.2.16
  src/sys/conf/newvers.sh                                  1.69.2.15.2.15
  src/sys/kern/sys_pipe.c                                   1.184.2.2.6.2
RELENG_7
  src/sys/kern/sys_pipe.c                                       1.191.2.5
RELENG_7_2
  src/UPDATING                                             1.507.2.23.2.4
  src/sys/conf/newvers.sh                                   1.72.2.11.2.5
  src/sys/kern/sys_pipe.c                                   1.191.2.3.4.2
RELENG_7_1
  src/UPDATING                                             1.507.2.13.2.9
  src/sys/conf/newvers.sh                                   1.72.2.9.2.10
  src/sys/kern/sys_pipe.c                                   1.191.2.3.2.2
- -------------------------------------------------------------------------

Subversion:

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/6/                                                         r193893
releng/6.4/                                                       r193893
releng/6.3/                                                       r193893
stable/7/                                                         r193893
releng/7.2/                                                       r193893
releng/7.1/                                                       r193893
- -------------------------------------------------------------------------

VII. References

The latest revision of this advisory is available at
http://security.FreeBSD.org/advisories/FreeBSD-SA-09:09.pipe.asc
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